Blow moulding machines for shaping plastics material pre-forms to form plastics material containers have long been known from the prior art. It is customary for apparatus of this type to have a plurality of blow moulds which in each case form a cavity, inside which the plastics material pre-forms are capable of being shaped to form containers, inside which pre-forms of plastics material (plastics material pre-forms) are expanded to form plastics material containers. In order to expand the plastics material pre-forms, the apparatus has a pressure-stressing device which acts upon the plastics material pre-forms with a medium such as for example compressed air. As a result, the plastics material pre-form is stretched both radially and in the longitudinal direction and is pressed against an inner wall of the blow mould bounding the cavity. In order to support the stretching in the longitudinal direction of the plastics material container, blow moulding machines usually have a stretch rod. Further plants for treating the containers, such as for example disinfecting devices, filling plants, closing means and the like, are usually present downstream with respect to these blow moulding devices.
For the sake of a better use of the gas over-pressure by which the plastics material pre-forms are expanded in the blow moulds to form plastics material containers, it is provided in some blow moulding machines that the over-pressure still present in the moulded plastics material container is not allowed to escape in an uncontrolled manner but is fed back and the gas is used again. This can be particularly advantageous for example if the plastics material pre-forms are first of all acted upon at a lower gas pressure in a blow moulding machine in order to carry out a preliminary stretching (possibly in parallel with the stretching of the plastics material pre-form by means of a stretch rod). This lower gas pressure can be for example the waste gas pressure from the final stretching process of other plastics material containers. In this way, it is possible to use the over pressure remaining in the stretched containers and thus to increase the efficiency of the blow moulding machine. On account of a recycling of blowing air inside the machine in this way it is possible for stretching air or preliminary blowing air no longer to have to be supplied from the outside.
In particular, in the case of modern blow moulding machines with very high throughput performance, the use of the gas pressure remaining in the plastics material containers is reasonable and economically advantageous. On account of the possibility of reducing the pumping power for producing the over-pressure, the operating costs can be lowered and emissions can be reduced. In this way it is possible for the air recovered by recycling processes of this type to be collected in an annular duct and to be used again for blowing the following containers.
Conveying the media back in order to act upon the plastics material pre-forms with pressure carries the risk, however, that impurities for example from the pre-forms may be taken along with the medium and thus that a plurality of blow moulds may be contaminated. This is critical in particular in the case of blow moulding machines with an increased hygiene level and in this case is particularly hazardous with respect to microbiological impurities, since in this way possibly harmful micro-organisms up to pathogens can penetrate into a large number of plastics material containers and thus even into the product which is filled into the moulded plastics material containers.
Accordingly, the object of the present invention is to provide a gas preparation device which makes it possible to clean the gas flows—in particular passing between a reservoir and a blow mould—in a blow moulding machine. In particular, microbiological impurities and residues of disinfecting/sterilizing agents should be removed or at least a portion of them should be significantly reduced. In addition, an object of the present invention is to make available a method of cleaning the gas flows passing between a reservoir and at least one blow mould in a blow moulding machine.